linux-kernel - Re: [PATCH] cifs: remove misleading strncpy: each name has length

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Message-ID: <87zk5pl83b.fsf@rho.meyering.net>
Date:	Mon, 20 Aug 2012 20:41:12 +0200
From:	Jim Meyering <jim@...ering.net>
To:	linux-kernel@...r.kernel.org
Cc:	Steve French <sfrench@...ba.org>, linux-cifs@...r.kernel.org,
	samba-technical@...ts.samba.org
Subject: Re: [PATCH] cifs: remove misleading strncpy: each name has length < 16

Jim Meyering wrote:

> From: Jim Meyering <meyering@...hat.com>
>
> Each of the protocols[i].name strings (statically declared above)
> has length less than 16, so this use of strncpy is misleading:
>   strncpy(pSMB->DialectsArray+count, protocols[i].name, 16);
> Besides, if a new name were added with length N >= 16, the existing
> strncpy-using code would be buggy, creating a ->DialectsArray buffer
> containing N-16+1 unset bytes where the NUL terminator should have
> been.  Instead, traverse the name only once go get its length,

s/go/to/, of course.

> use a BUG_ON assertion to enforce the length restriction
> and use memcpy to perform the copy.
>
> Signed-off-by: Jim Meyering <meyering@...hat.com>
> ---
>  fs/cifs/cifssmb.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
> index 074923c..16a9018 100644
> --- a/fs/cifs/cifssmb.c
> +++ b/fs/cifs/cifssmb.c
> @@ -441,8 +441,10 @@ CIFSSMBNegotiate(const unsigned int xid, struct cifs_ses *ses)
>
>  	count = 0;
>  	for (i = 0; i < CIFS_NUM_PROT; i++) {
> -		strncpy(pSMB->DialectsArray+count, protocols[i].name, 16);
> -		count += strlen(protocols[i].name) + 1;
> +		size_t len = strlen(protocols[i].name);
> +		BUG_ON(len >= 16);
> +		memcpy(pSMB->DialectsArray+count, protocols[i].name, len + 1);
> +		count += len + 1;
>  		/* null at end of source and target buffers anyway */
>  	}
>  	inc_rfc1001_len(pSMB, count);
--
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